WEATHER CHARACTERISTICS AT OBSERVATORY CANDIDATE SITES IN WEST TIBET

Abstract

The high plateaus in west China may provide suitable sites for astronomical observations with theinstitute’s middle-range telescopes and possibly with larger telescopes. Under China-Japan collaborationsfor site survey in west China, we have been conducting searches for good sites and monitoring theircharacteristics over several years. As recent results of our site survey show, sites in west Tibet arerevealed with a high possibility of good astronomical observations.Weather characteristics at Gar in Ali, Tibet, show its high clear-sky ratios, especially in winter, com-parable to Mauna Kea, Hawaii. But it has some wind problem in winter, where stronger wind speeds,over 20m/sec, occur frequently even though the sky is clear. To nd calmer sites, we have conductednumerical simulations for the Ali area using the Japan Meteorological Agency NonHydrostatic Model.We have found another site, named ZoZo Hill, near Gar. We will continue to monitor the Gar site toclarify weather characteristics over the whole year and hopefully start to negotiate for site monitoring atZoZo Hill this year.Key words: international collaboration, site test, telescope site, west Tibet1. WEST TIBET AS AN IMPORTANT LONGITUDI-NAL LOCATION FOR GLOBAL ASTRONOMICALOBSERVATION NETWORKAs west China is indicating its importance in playinga role for the global astronomical observation network(Yao 2005), we have been conducting astronomical site-monitorings at three sites in west China; Karasu (Xin-jiang Uighur), Oma (Tibet) and Gar/Ali (Tibet) undera China-Japan Astronomical Collaboration since 2007(Sasaki et al., 2008; Yao et al., 2011; Sasaki et al., 2011).2. ASTRONOMICAL SITE MONITORINGSeveral astronomical site-monitoring instruments havebeen deployed at the sites. At the Oma and Gar site,cloud monitoring cameras have revealed excellent skyconditions, especially in winter. Gar has shown betterweather conditions than Oma.On the other hand, strong winds that have been ob-served at the current monitoring site, Gar, in winter mayseriously a ect the number of observable nights (Figure1), as the imaging capabilities of telescope optics wouldbe reduced due to turbulence caused by stronger windhttp://pkas.kas.orginside the telescope dome by applying the criteria forwind speed